1. Technical Field
The present invention pertains to pressurized infusion and temperature control apparatus or systems for infused liquids. In particular, the present invention is directed toward pressurized infusion of liquids into a patient and/or temperature control of that liquid during infusion into a patient.
2. Discussion of Prior Art
Generally, intravenous (I.V.) solution or other liquids are infused into a patient by disposing a liquid-filled bag containing intravenous solution or other liquid on a pole structure to permit gravitational forces to direct liquid from the liquid-filled bag through an intravenous or other tube into the patient. However, gravitational forces may be insufficient to drive certain viscous liquids, such as refrigerated blood, into the patient, or drive liquids into the patient at a sufficient rate. The prior art has attempted to overcome the aforementioned inadequacies of gravitational forces by applying pressure to the liquid-filled bag to enhance liquid flow from the liquid-filled bag to the patient. For example, U.S. Pat. No. 4,090,514 (Hinck et al) discloses a pressure infusion device including a bladder wherein the device encases a liquid-filled bag with the bladder surrounding at least eighty percent of that bag. Upon inflation of the bladder, liquid within the liquid-filled bag is infused under pressure to a patient. Further, U.S. Pat. No. 4,551,136 (Mandl) discloses a pressure infuser including an inflatable bladder that wraps about a liquid-filled bag. The bladder includes a vertical strip at each end and a strap that wraps about the bladder and liquid-filled bag. The vertical strips overlap to provide a complete wrap about the liquid-filled bag, while the strap maintains the overlapping strip portions in contact. The bladder is inflated to a desired pressure whereby pressure is applied by the bladder to the liquid-filled bag to infuse liquid into a patient.
The Hinck et al and Mandl devices suffer from several disadvantages. In particular, the Hinck et al device includes a bladder that substantially surrounds a liquid-filled bag, however, the bladder may not expand sufficiently to apply adequate pressure to the liquid-filled bag when small volumes of liquid are present within the liquid-filled bag, thereby operating less efficiently when smaller volumes of liquid reside within the liquid-filled bag and requiring premature replacement of the liquid-filled bag prior to utilization of liquid within that bag. Similarly, the Mandl infuser utilizes a strap to maintain a bladder about a liquid-filled bag wherein pressure exerted by the bladder on the liquid-filled bag is focused substantially coincident the strap, thereby operating less efficiently, especially when smaller volumes of liquid reside within the liquid-filled bag, since various pressures are applied to different portions of the liquid-filled bag (e.g., the bladder portions disposed near the strap apply the greatest amounts of pressure, while the bladder portions disposed furthest from the strap apply the least amounts of pressure), and requiring premature replacement of the liquid-filled bag prior to utilization of liquid within that bag. In other words, when the liquid-filled bags become partially depleted and thin, the bladders of the Hinck et al and Mandl devices may not maintain adequate pressure on the thinner bags for infusion of liquid into a patient. Further, the bladders of these devices generally include certain dimensions, thereby only being compatible or satisfactorily operable with liquid-filled bags of a particular size. Moreover, the Hinck et al and Mandl devices do not thermally treat the liquid-filled bags in any manner during infusion.
In addition to providing pressurized infusion as described above, it is desirable during surgical procedures to maintain a patient's body temperature at approximately 98.6° F. or 37° C. (i.e., normal body temperature) to avoid hypothermia and complications that may arise with minute decreases in body temperature (e.g., decreases of approximately 2-3° C.). Further, infusion into a patient of liquids having temperatures below the normal body temperature may produce further complications, such as shock, cardiac dysfunction, increased coagulation time, and in certain patients, clumping of blood cells.
In order to avoid hypothermia and other complications described above, warmers are typically employed during surgical or other medical procedures to maintain the temperature of infused liquids at or near body temperature. Generally, prior art warmer systems employ various techniques to heat infused liquids. In particular, infused liquid may be directed within tubing or a bag through a solution bath (e.g., warmed liquid); infused liquid may be directed about a tube through which warmer liquid flows in an opposing direction; infused liquid may traverse tubing or be stored in a bag placed proximate heating plates; infused liquid may be disposed in a bag placed about a heating element; infused liquid may be warmed by a heat exchanger in the form of a cassette placed between heating plates; or infused liquid may be warmed via heated air or microwave energy. For example, U.S. Pat. No. 1,390,500 (Christian) discloses a flexible water heater and dripper wherein water and other liquid flow from a container and are heated while traversing a flexible heating element having a conduit. The heating element includes resistance coils and is connected to a rheostat having a sliding member to control current to the heating device to provide a desired degree of heat.
U.S. Pat. No. 1,726,212 (Bucky) discloses an irrigator including a container filled with liquid having a heater for heating the liquid to a desired temperature. A bulb pumps air into the container to produce a pressure that drives the liquid through tubing to an irrigation site.
U.S. Pat. No. 1,995,302 (Goldstein) discloses an adjustable heating infusion apparatus wherein a flexible tube conveying fluid is heated via an electric resistance wire spirally wound about the tube outer surface. The wire spirals are more concentrated at a tube proximal end to raise liquid temperature toward a desired level, while the remaining windings maintain the liquid temperature at substantially that desired level. A thermostatic current control regulates current to the resistance wire to maintain a predetermined temperature.
U.S. Pat. No. 3,247,851 (Seibert) discloses an apparatus for applying liquids to the body wherein a heating unit extends along a length of a tube to heat liquid as the liquid flows from a receptacle. The heating unit includes heating wires and a thermostat to heat the liquid in the tube.
U.S. Pat. No. 5,250,032 (Carter, Jr. et al) discloses a heater for in vivo blood infusion including a housing having a channel for receiving a portion of an intravenous tube. A heating element is mounted proximate a slot disposed within the channel to heat the tube wherein the heating element is controlled by a control circuit and powered by batteries. The control circuit controls the heating element in response to sensed temperatures.
U.S. Pat. No. 5,254,094 (Starkey et al) discloses a physiological fluid warmer including two chambers having coils for fluid to flow, while a warming liquid flows through the chambers along the coils in a direction opposite to the fluid flow. The fluid warmer may be controlled by a microprocessor to operate in response to either fluid or warming liquid temperature.
The prior art warmer systems described above suffer from several disadvantages. In particular, the prior art warmer systems heating liquid within an intravenous or other tube tend to employ and control a single heating element disposed along the tube, thereby limiting control accuracy of the liquid temperature and typically producing hot spots (e.g., certain sections of the tube may become warmer than other sections of the tube) along the tube. Some of the prior art warmer systems require pre-heating of a liquid-filled bag prior to use in and external of those systems, thereby requiring additional time to heat the liquid. Further, the prior art warmer systems heating liquid within an intravenous or other tube typically rely on gravitational forces to direct the liquid to the patient. These gravitational forces may be inadequate to produce desired flow rates or enable flow of viscous solutions as described above. Moreover, certain prior art warmer systems heat liquid flowing within an intravenous or other tube at a site located a substantial distance from the patient entry point, thereby permitting heated liquid to cool by the time the heated liquid reaches the patient. In addition, the prior art warmer systems typically control liquid heating based solely on temperature measurements of the liquid, thereby limiting control options and providing for less accurate control. The prior art warmer systems typically maintain activation of heating elements in cases of excessive liquid or heating element temperatures or interruptions in liquid flow, thereby enabling the heating elements to heat the liquid to temperatures beyond the liquid utilization temperature range and possibly injure a patient and/or damage an intravenous or other tube. A further disadvantage of the prior art warmer systems heating liquid within an intravenous or other tube is that the temperature of liquid contained within a liquid-filled bag or receptacle is typically substantially below a desired temperature, thereby requiring significant heating of the liquid during infusion as the liquid traverses the tube.